1. The Field of the Invention
This invention broadly relates to an improved process for treating solid fossilized carbonaceous fuels with an aqueous medium in the presence of a novel catalyst. The invention further relates to the removal of combustible sulfur and nitrogen compounds and other undesirable constituents from solid fossilized fuels, and the solubilization and recovery of metal and non-metal values therefrom. In one of its more specific variants, the invention is concerned with the preparation of solvent soluble organic compounds and an activated solid carbonaceous residue from solid fossil fuels. In another variant, the invention is concerned with the solubilization of solid carbonaceous fossil fuels or components thereof in an aqueous medium containing the aforementioned catalyst to thereby produce a novel aqueous solution which has highly unusual and unexpected properties.
2. The Prior Art
Solid fossilized carbonaceous fuels such as coal, lignite and peat are products of the gradual decomposition of vegetable matter without free access of air. Bituminous and anthracite coal, and to some extent lignite, are thought to have been formed in the presence of moisture at elevated temperature and pressure. Most authorities believe that coal passes through successive stages of peat, lignite or brown coal, sub-bituminous and bituminous or soft coal, and anthracite or hard coal under conditions of increasing temperature and pressure. The carbon content increases on a weight percent basis as the vegetable matter is transformed from peat into anthracite coal, and much of the carbon is combined with other elements such as hydrogen, sulfur, nitrogen and alkali metal, alkaline earth metal or heavy metal values.
Solid fossilized carbonaceous fuels and especially coal comprise high molecular weight three-dimensional cyclic structures which contain predominantly six membered rings. For example, it is known that coal contains bitumin and humin which have large, flat, aromatic lamellar structures that differ in molecular weight, degree of aromaticity, oxygen content, nitrogen content and the degree of cross-linking. Volatile matter, fusain, mineral matter, moisture, pyritic sulfur, inorganic sulfates, and organic sulfur and nitrogen compounds also are present. Fusain is a mineral charcoal which is consumed during burning in the presence of sufficient oxygen for complete combustion and the mineral matter remains behind as ash. Fusain, mineral matter and inorganic sulfates do not contribute to atmospheric pollution upon complete combustion of the coal. However, the presence of combustible sulfur such as pyritic sulfur and organic sulfur compounds results in the formation of sulfur oxides which, upon reaction with atmospheric moisture, produce highly corrosive sulfurous acid and/or sulfuric acid. Combustible nitrogen compounds also present similar problems. As a result, urban areas have strict air pollution regulations which require that the sulfur content of solid fossilized carbonaceous fuels be reduced to about 0.5% by weight or less of combustible sulfur so as to control atmospheric pollution.
The prior art processes for reducing the combustible sulfur content of solid fossilized carbonaceous fuels are expensive and require elaborate equipment, costly chemicals or vigorous reaction conditions such as high temperatures and pressures. As a result of the inherent deficiences of the prior art desulfurization processes, the coal industry has long sought an efficient low-cost process for removing combustible sulfur from coal.
Solid fossilized carbonaceous fuel also has been treated heretofore to produce organic chemicals, solid carbonaceous products such as coke and activated carbon, and liquid hydrocarbon fuels. For example, coke is produced by heating coal at about 1,000.degree.-1,300.degree. F., in a retort. The coke thus produced is a hard porous residium consisting largely of carbon admixed with mineral ash and other nonvolatile constituents of the original coal. Volatile byproducts are produced such as coal gas, coal tar, coal tar chemicals and ammonia. The low temperature carbonization of coal at temperatures of about 500.degree.-700.degree. F. produces products which differ substantially from those obtained at the higher carbonization temperatures. Nevertheless, both processes involve cracking of the large molecules of the coal to produce a solid residue consisting largely of carbon and mineral ash, and volatile constituents such as coal gas and normally liquid byproducts.
Liquid and gaseous fuels have been produced from coal by the Bergius Process. The early Bergius process usually consisted of mixing powdered coal with heavy tar from previous runs and approximately 5% of iron oxide as a catalyst. The pasty mass thus produced was heated with hydrogen at about 450.degree.-490.degree. F. for around two hours at a pressure of approximately 3,000 pounds per square inch. There has been much research in this area in an effort to produce petroleum-like materials from coal. The more recent processes use different and more effective catalysts and the reaction mixture is either in liquid or gaseous phase. In all of the processes, the coal is subjected to drastic processing conditions.
Activated carbon has been produced heretofore from coal using a combination of high temperature and various chemicals to convert the raw coal into an activated carbon residue. Some processes involve subjecting finely divided raw coal to high pressures and temperatures and treatment in the presence of steam alone or in combination with chemicals. In the latter process, the pressure is often reduced very quickly causing the steam that has penetrated the coal particles to expand rapidly. This ruptures bonds within the coal particles and increases the available surface area and porosity.
There are large deposits of solid fossilized carbonaceous materials in the United States which contain small percentages of valuable metal values or non-metal values. Examples of these deposits include uranium-bearing lignite and coal which are estimated to contain a substantial percentage of all known uranium reserves discovered to date. Often other valuable metal values are present such as molybdenum, cobalt, zirconium, germanium and the like. Selenium and other valuable non-metal values also are present in some deposits. Entirely satisfactory prior art processes were not available heretofore for solubilizing and recovering these metal values and/or non-metal values. For example, one prior art practice involves burning heavy metal-bearing lignite and recovering the ash which contains the metal values, and then processing the ash into a commercial form of the metal values for sale such as uranium oxide, vanadium oxide, molybdenum oxide, and the like. In accordance with another prior art practice, the fossil fuel is heated in a closed system in the presence of hydrogen and under drastic reaction conditions including high temperature and pressure, with or without a catalyst, to produce a liquid petroleum-like material and a solid residue which contains the metal values. The residue is separated from the liquid and gaseous products, and is further processed in accordance with prior art practices to recover the metal values in the form of a marketable commercial product.
All of the processes discussed above which have been used heretofore for converting solid fossilized carbonaceous fuels into more valuable products involve the use of elaborate equipment, numerous processing steps, large quantities of processing chemicals which are not readily recycled, and drastic reaction conditions. As a result, the processes available heretofore have been costly to practice and in some instances uneconomical.
It has also been proposed to use solid carbonaceous fossil fuels as fertilizer, and the presence of fungistatic and bacteriostatic ingredients has been suggested. However, entirely satisfactory processes were not available heretofore to produce acceptable commercial products on a reproducible basis.